1. Field of the Invention
This invention relates to an electrophotographic photosensitive member, particularly to an electrophotographic photosensitive member having excellent mechanical strength, surface lubricity, humidity resistance and image characteristic.
2. Related Background Art
An electrophotographic photosensitive member is demanded to be provided with certain sensitivity, electrical characteristic, optical characteristic corresponding to the electrophotographic process for which it is to be applied, and further in a photosensitive member which is used repeatedly, since electrical, mechanical external forces are directly applied such as corona charging, toner development, transfer onto paper, cleaning treatment, etc. on the surface layer of the photosensitive member, namely the layer which is the most remotest from the substrate, durability to such treatments is demanded. More specifically, durability to generation of abrasion or flaws on the surface by sliding, and also to deterioration of the surface with ozone generated during corona charging under highly humid conditions, etc. has been demanded.
On the other hand, there is also the problem of toner attachment onto the surface layer by development of toner, repetition of cleaning, and to cope with this problem, it has been demanded to improve cleaning characteristics of the surface layer.
For satisfying the demanded characteristics as mentioned above, various methods have been investigated, and among them it is effective to disperse a solid lubricating agent, particularly a fluorine type resin powder in the surface layer of the photosensitive member, as disclosed in Japanese Patent Laid-Open Application No. 57-747478, U.S. Pat. Nos. 4,030,921 and 4,663,259. By dispersing fluorine type resin powder, durability to flaws, surface cleaning characteristics, abrasion, etc. can be improved, and it is also effective for prevention of surface deterioration of the photosensitive member under highly humid conditions because it can improve water repellency, mold releasability of the surface of the photosensitive member.
Also, when a layer containing fluorine type resin powder dispersed therein is provided as a protective layer, the charge transport material or the charge generation material which is susceptible to deterioration with ozone is separated from the surface, whereby durability can be further improved.
However, when a coating solution containing fluorine type resin powder is coated to form a coating in order to form the surface layer of the photosensitive layer, the outermost surface of the coating formed has no fluorine type resin powder exposed thereon, but a binder resin covers the surface of the coating. For this reason, the effect as described above when fluorine resin powder is dispersed will not appear at all at the initial stage of using the photosensitive member. As the result, for example, troubles such as fusion between the cleaning blade and the surface of the photosensitive member, damage of the drum surface by reverse rotation of cleaning blade, etc. will frequently occur. For prevention of such troubles, measures such as special spraying of toner or lubricating powder, artificial cutting of the surface, etc. must be taken during usage, whereby the cost cannot but be increased with respect to installation or labor to involve a problem in practical application.